Electrolytic cell with slotted anode

ABSTRACT

NOVEL ANODES FOR USE IN ELECTROLYTIC CELLS HAVE GENERALLY VERTICAL SLOTS IN THE LOWER PORTION OF THE ANODE WHICH ARE OPEN AT THE BOTTOM OF THE ANODE AND CLOSED AT THE ENDS OF THE SLOTS WITH A PLURALITY OF GAS CONDUCTING CHANNELS CONNECTING THE TOP OF THE SLOTS WITH THE UPPER SURFACE OF THE ANODE.

Jan; 2 6,V 1971 P. A. DANNA 3,558,464

ELECTROLYTIC CELLl WITH SLOTTED ANODE med March 25. 196e /5 ,/41 i, HIMWZWI VWM j f/7-/Z AZ- FIG-6 Am di UG 1 Pfffm AGENT United States Patent O 3,558,464 ELECTROLYTIC 'CELL WITH SLOTTED ANODE Peter A. Danna, Milford, Conn., assignor to Olin Corporation, a corporation of Virginia Filed Mar. 25, 1968, Ser. No. 715,688 Int. Cl. C22d l 04 U.S. Cl. 204-219 10 Claims ABSTRACT F THE DISCLOSURE of the anode.

This invention relates to novel anodes suitable for use in electrolytic cells, particularly cells of the liquid cathode type and, more particularly, in mercury cathode electrolytic cells. The use of the anodes of this invention in other cells of similar construction is also contemplated.

Horizontal mercury cells usually consist of an enclosed, elongated trough sloping slightly towards one end. The cathode is a flowing layer of mercury which is introduced at the higher end of the cell and flows along the bottom of the cells toward the lower end. The anodes are generally composed of rectangular blocks of graphite suspended from conductive lead-ins, for example, graphite or protected copper tubes or rods, in such a manner that the bottom of the graphite anode is spaced a short distance above the ilowing mercury cathode. The bottom and sides of the trough are generally steel with a corrosion resistant hard rubber lining on the sides and under the cover. Concrete, stone or other non-conducting material may also be used for the sides. The lining may comprise concrete which is further coated with resin, or has natural stone set in the concrete lining.

In the operation of this type of cell, the electrolyte is an aqueous solution of any electrolyte which upon electrolytic decomposition will give the products desired. The electrolyte is introduced at the upper end of the cell and flows toward the lower end of the cell. Direct current passes through the solution between the anodes and the mercury cathode. When sodium chloride is the electrolyte, chlorine is formed at the anodes and passes to the top of the cell and out through an opening in the cell cover. Sodium is formed at the cathode as an amalgam with the mercury cathode. The sodium amalgam is withdrawn at the lower end of the cell, cycled to a decomposer packed with graphite where it is contacted with water to form sodium hydroxide, hydrogen and mercury. The mercury is recycled to the cell for reuse as the cathode. It will be understood that brines of other electrolytes, such as potassium chloride, barium chloride, lithium chloride, sodium sulfate and other brines may also be electrolyzed in such cells.

In these cells, chlorine bubbles adhering to the anode Surfaces reduce the active surface in contact with the brine and contribute substantially to the total resistance in the cell. This increases the voltage required to force the electric current to ilow through the cell especially at high current densities. Various anode designs are known in the art to facilitate the removal of bubbles and collection of the gas, including drill holes, channels and slots variously arranged. See, for example U.S. Pats. 3,062,733; 3,174,923 and 3,268,427.

What appears not to have been discerned by the art is the fact that in slotted and drilled anodes, part of the brine is lifted through the drill holes by the gas bubbles and this brine ows across the top of the anode. At the next downstream gap between anodes, much of the brine enters the slots in the next anode without traversing the anode-cathode gap Where the llow of brine might dislodge the bubbles. The improved anode of this invention avoids this shortening of the path of brine flow in the cell and forces the entire flow of brine to traverse the anodecathode gap, effecting greatly improved dislodging of gas bubbles on the lower surface of the anode and materially lowering the voltage required to force the current through the cell.

The anode of the present invention has generally vertical slots arranged in the lower portion of said anode, said slots being open at the bottom of said anode and closed at the ends of said slots and a plurality of gas channels connecting the top of said slots with the upper surface of said anode.

The closed end slots are formed in the anodes of the present invention in any suitable manner. Slots are formed in the lower part of the anode without slotting the ends of the anode by means of a milling machine, circular saw or chain saw. Alternatively, slots are cut through the ends of the anode and the ends are closed by end plates attached by any suitable means, including bolts, screws, pegs or chlorine-resistant adhesive, preferably electrically conductive adhesives. In still another alternative, the open slots are closed by plugs or wedges inserted from the ends or from the top of the anode to close the slots. The material for end plates or plugs is suitably graphite, titanium, Teon or other suitably chlorine-resistant material. In another alternative, the ends of the slots are suitably closed by lling with chlorine-resistant cements, for example, silicone rubber cement.

Accompanying FIGS. 1-7 illustrate the invention. FIG. l shows an end of an anode, partly in section and partly in view where 11 is the anode body, 12 is one of a plurality of slots in the anode and 13 is an adhesively applied plate covering the ends of slots 12. Gas channels are indicated at 14.

FIG. 2 is a section of the anode of FIG. l cut on a plane through the middle of a slot as indicated by line 2-2. The same structures have the same numbers as in FIG. 1.

FIG. 3 is similar to FIGS. l and 2 but the plates 14 are applied by screws 15 instead of adhesively.

FIG. 4 shows another modification of the invention in which slots 12, originally cut through the anode block and open at both ends, are closed by wedges 16.

FIG. 5 shows another modification of the invention in which slots 12, originally cut through the anode block and open at both ends, are closed by plugs 17 inserted in holes through anode 11 from top to bottom.

FIG. 6 shows a modification of` the invention in which slots 12 are cut in anode 11, leaving ends 18 of the anode as integral parts of anode 11.

FIG. 7 shows a modification of the invention with slots 12 cut by a circular saw leaving ends 18 of the anode as integral parts. In this embodiment, gas channels 14 have various lengths.

EXAMPLE I The test cell had brine inlet and outlet, mercury inlet and amalgam outlet chlorine outlet, an electrical lead to the ilowing mercury cathode and parallel leads to each of two anodes. Both anodes were 24 inches long by 9 inches wide by 6 inches thick with longitudinal slots cut in the bottom substantially as shown in FIG. 1 but without cover 13.

Brine was electrolyzed in the cell at 1000 amperes for 2 to 3 hours using both anodes to bring ow rates, temperature, brine concentration, pH and other variables to a steady state. The brine level was maintained at 4% inches above the tops of the anodes. Cell current was reduced to 200 amperes, the test anode was disconnected and the current on the control anode was increased to 2000 amperes during approximately 2 minutes. Current and voltage were recorded on an X Y plotter. This procedure provided a reference voltage for the control anode at any amperage over the range from 200 to 2000 arnperes under the conditions prevailing in the cell. The current was again reduced to 200 amperes. The test anode with slots open was reconnected and the control anode was disconnected. The current was raised and voltage measured and recorded using the test anode in the same manner as with the control anode. At any particular amperage, the voltages provided a standard difference between the test anode and the control anode under the conditions of cell operation. The same procedure was repeated, including the measurement of current and voltage using the control anode and substituting the same test anode having the slots sealed at the ends with silicone rubber cement. At any amperage, the voltage difference between the test anode with slots closed and the control anode was compared with the voltage difference between the test anode with slots open and the control anode. The resulting voltage difference measured the effect of closing the slots in the test anode and eliminated all other variables. The results are shown in Table I and demonstrate an improvement due to closing the slots of 0.11 and 0.10 volt per anode at 1500 and 2000 amperes, respectively. In a plant consisting of 250 cells, each with 50 anodes the resulting voltage reduction amounts to an annual saving in power cost of $54,000.

Using the same cell and the same anodes as described in Example I but maintaining the brine level one inch above the tops of the anodes, the test procedure described in Example I was repeated to eliminate the eiect of all variables except that of brine depth and closing the slots, The resulting data are presented in Table II.

TABLE II Test conditions Voltage Current, amps l, 000 1, 500 2, 900 Test anode slots open Test anode 4. 40 5.05 5. 78 Control anode 4. 28 4. 92 5. 55

Diterence +0. 12 +0. 13 +0. 23

Test anode slots closed:

Test anode 4. 32 4. 98 5.60 Control :mode 4. 40 5. 10 5. 80

Dillen-ence- 0.08 0.12 0.

Eller-t of closlng slots 0. 20 0. 25 0. 43

4 These data show that the advantage of closing the anode slots is more pronounced using the lower brine level above the anodes but the effect is significant even with deep coverage of the anodes by brine as in Example I.

EXAMPLE III The procedure of Example I was repeated using anodes dilfering in slot width and number and hole pattern. The testing procedure of Example I was repeated, eliminating the effect of all variables except that of closing the slots. The brine level was 4% inches above the tops of the anodes. The data are presented in Table III and show significant voltage reductions due to closure of the ends of the slots.

The procedure of Example I was repeated using the same anodes as in Example III but maintaining the brine level 1 inch above the tops of the anodes. Similar advantageous voltage reduction due to end closure of the 5 slots is shown by the data Table 1V.

TABLE IV Test conditions Current, amps Test anode slots open:

Test anode Control anode.

Diterenee Test anode slots closed:

Test anode 4.40 4.95 5.55 Control anode 4. 38 5.00 5.70

Dierence +9.02 0.05 0.15

Etect of closing slots 0.23 0.42 0. 57

What is claimed is: 1. In a mercury cathode electrolytic cell for brine electrolysis, an anode having two closed side surfaces, two closed end surfaces and top and bottom surfaces, said anode having generally vertical slots arranged in the lower portion of said anode, said slots being open at the bottom surface of said anode and closed at the end surfaces of said anode and a plurality of gas channels connecting the top of said slots with the upper surface of said anode.

2. An anode as claimed in claim 1 in which the means for closing said slots are inserted into said slots.

3. An anode as claimed in claim 2 in which said means is a wedge.

4. An anode as claimed in claim 2 in which said means is a plug inserted through the top of the anode and extending to the bottom of said anode.

5. An anode as claimed in claim 1 in which the ends of said slots are covered by a plate xedly attached to said anode.

6. An anode as claimed in claim 5 in which said plate is adhesively attached.

7. An anode as claimed in claim 5 in which the means attaching said plate are threaded means.

8. An anode as claimed in claim 1 in which said slots are shorter than the dimension of the anode in which said slots extend and said ends are integral with said anode.

References Cited UNITED STATES PATENTS 3,310,482 3/1967 Bon et al. 204-250 3,268,427 8/ 1966 Schucker 204-219 3,174,923 3/ 1965 Golden et al 204-284 6 Lynn et al. 204-284 Sanders 204-224 Williams 204-284 Burnett 219-69 5 JOHN H. MACK, Primary Examiner S. S. KANTER, Assistant Examiner U.S. Cl. X.R. 

